1. Compass Basics and Types Doug “Due North” Millar K6JEY

2. Types Boy Scout type “Lensatic” Sighting- has a mirror and/or prism Transit- for surveyors Solar compass- for moving vehicles GPS- Fluxgate Compass- need frequent calibration.

3. Compass Basics There are a number of types of compasses, but for our needs a “sighting” or lensatic type is best. There are a number of types of compasses, but for our needs a “sighting” or lensatic type is best. Look for Fluid filled, jeweled movement Fluid filled, jeweled movement Declination adjustment Declination adjustment Good mechanics and stability. Good mechanics and stability.

4. WWI Military Lensatic Type

5. Calibration Problems To find the local isogonic variation look on Aeronautical charts or airport diagrams. To find the local isogonic variation look on Aeronautical charts or airport diagrams. The variation here changes by.1 degree/year. Long Beach is 13.2 W and Camarillo is 14.7 Long Beach is 13.2 W and Camarillo is 14.7 Setting the variation has to be done accurately. Setting the variation has to be done accurately. Matching the compass with true North is a mechanical problem. Matching the compass with true North is a mechanical problem. But local man-made and natural magnetic anomalies are the greatest error. But local man-made and natural magnetic anomalies are the greatest error.

6. Airport Diagram Has isogonic variation per year and dated measurement.

7. Sighting Compass Worse than1deg. Sunto $50

8. Below ½ Degree Below this level of accuracy there are all kinds of variables that come into play and an accurate heading is hard to know. Try for 1deg accuracy. One idea is to use a Go To astronomical mount and align it with known objects. Another is to use digital setting circles.

9. The Bad, Good and Strange Most inexpensive lensatic types are useless. They don’t settle well and calibration moves. Sighting compasses with a mirror are very good if the fluid dampens the movement and they are settable. Good ones are $$$ The Morin is excellent but does not have dec. adjustment. Also $$$$ The solar compass- great till it’s dark

10. A cheap Lensatic type Read Wrong Guessometer

11. Typical Inexpensive Compass with few Extras. Accuracy worse than 1deg.

12. Excellent sighting type A Brunton 8099 <1deg $70 plus

14. Morin sighting type Better than 1deg about $100

16. Solar Compass with Gnomon Used for vehicles in motion.

17. Best Bang for the Buck Chinese Military lensatic type available for About $20 on Ebay

18. The Chinese Military lensatic just shown has a number of Important features. Magnified viewer with diopter adjustment Fluid dampened card Excellent sighting and mirror mechanism Better than 1 deg resolution Built in level Built in photo tripod mount Case Smooth setting bezel and isogonic offset.

19. Conclusion A good enough sighting compass should cost less than $50. Don’t put up with a hard to use read-wrong guessometer. Don’t expect more than your calibration and information can deliver. If you are within a degree that may be about as good as you can do. Any further and results go up in a linear fashion and money goes up in an exponential fashion.

20. I brought one of each type to try out and to look at.

21. References Accuracy considerations: http://www.geocities.com/magnetic_declination/#COMPE NSATE Compass use from a boater’s point of view. http://books.google.com/books?id=nfWSxRr8VP4C&pg= PA43&lpg=PA43&dq=isogonic+variation&source=web&o ts=z8ZKEZS2TI&sig=vP9TLCKMHCPoEWwZkmj8o1OY Dl8&hl=en&sa=X&oi=book_result&resnum=10&ct=result #PPA44,M1 http://books.google.com/books?id=nfWSxRr8VP4C&pg= PA43&lpg=PA43&dq=isogonic+variation&source=web&o ts=z8ZKEZS2TI&sig=vP9TLCKMHCPoEWwZkmj8o1OY Dl8&hl=en&sa=X&oi=book_result&resnum=10&ct=result #PPA44,M1 http://books.google.com/books?id=nfWSxRr8VP4C&pg= PA43&lpg=PA43&dq=isogonic+variation&source=web&o ts=z8ZKEZS2TI&sig=vP9TLCKMHCPoEWwZkmj8o1OY Dl8&hl=en&sa=X&oi=book_result&resnum=10&ct=result #PPA44,M1

22. Thanks for Listening K6JEY “Due North Doug”